mm: fix -Wmissing-prototypes warnings

We get two warnings when build kernel W=1:

  mm/shuffle.c:36:12: warning: no previous prototype for `shuffle_show' [-Wmissing-prototypes]
  mm/sparse.c:220:6: warning: no previous prototype for `subsection_mask_set' [-Wmissing-prototypes]

Make the functions static to fix this.

Link: http://lkml.kernel.org/r/1566978161-7293-1-git-send-email-wang.yi59@zte.com.cnSigned-off-by: Yi Wang <wang.yi59@zte.com.cn>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shuffle.c

@@ -33,7 +33,7 @@ __meminit void page_alloc_shuffle(enum mm_shuffle_ctl ctl)
 }
 
 static bool shuffle_param;
-extern int shuffle_show(char *buffer, const struct kernel_param *kp)
+static int shuffle_show(char *buffer, const struct kernel_param *kp)
 {
 	return sprintf(buffer, "%c\n", test_bit(SHUFFLE_ENABLE, &shuffle_state)
 			? 'Y' : 'N');

mm/sparse.c

@@ -219,7 +219,7 @@ static inline unsigned long first_present_section_nr(void)
 	return next_present_section_nr(-1);
 }
 
-void subsection_mask_set(unsigned long *map, unsigned long pfn,
+static void subsection_mask_set(unsigned long *map, unsigned long pfn,
 		unsigned long nr_pages)
 {
 	int idx = subsection_map_index(pfn);